Method and apparatus for managing communication services for user endpoint devices

ABSTRACT

A system that incorporates teachings of the present disclosure may include, for example, an edge device having a controller to receive a Session Initiation Protocol (SIP) message from a user endpoint device (UE) requesting communication services, forward the SIP message to a network element of a Server Office, receive from the network element a first error message indicating communication services at the Server Office are unavailable, replace the first error message with a second error message, the second error message indicating a temporary unavailability of communication services, and transmit the second error message to the UE. Additional embodiments are disclosed.

PRIOR APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/542,192 filed Jul. 5, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/569,722 filed Sep. 29, 2009, which claims thebenefit of priority to U.S. Provisional Application No. 61/222,044 filedon Jun. 30, 2009. All sections of the aforementioned applications areincorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to user endpoint devicemanagement, and more specifically to a method and apparatus for managinguser endpoint devices in a communication network.

BACKGROUND

When a service provider of communications deploys a communicationsnetwork, there can be many challenges. Among them include withoutlimitation the cost of deployment, the cost of adding network equipmentto accommodate subscriber growth, maintenance of the network,serviceability of the network, and managing the addition of newsubscribers to the network—just to mention a few.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 depict illustrative embodiments of a communication system;

FIG. 3 depicts an illustrative embodiment of provisioning informationused by subscriber devices of the communication system of FIGS. 1-2;

FIGS. 4-5 depict illustrative embodiments of communication flow diagramsbetween the subscriber device and network elements of the communicationsystem;

FIG. 6 depicts an illustrative method operating in portions of thecommunication system of FIGS. 1-2;

FIGS. 7-10 depict illustrative embodiments of communication flowdiagrams between a UE and network elements of the communication systemof FIGS. 1-2 according to the method of FIG. 8;

FIG. 11 depicts an illustrative method operating in the Edge Device ofthe communication system of FIGS. 1-2; and

FIG. 12 depicts an illustrative diagrammatic representation of a machinein the form of a computer system within which a set of instructions,when executed, may cause the machine to perform any one or more of themethodologies disclosed herein.

DETAILED DESCRIPTION

One embodiment of the present disclosure entails an edge device having acontroller to receive a Session Initiation Protocol (SIP) message from auser endpoint device (UE) requesting communication services, forward theSIP message to a network element of a Server Office, receive from thenetwork element a first error message indicating communication servicesat the Server Office are unavailable, replace the first error messagewith a second error message, the second error message indicating atemporary unavailability of communication services, and transmit thesecond error message to the UE.

One embodiment of the present disclosure entails a user endpoint device(UE) having a controller to transmit to an edge device a SessionInitiation Protocol (SIP) message to request communication services, andreceive from the edge device a second error message indicating atemporary unavailability of communication services, wherein the edgedevice transmitted the second error message to the UE in place of afirst error message received from a Server Office indicating service isunavailable.

One embodiment of the present disclosure entails a computer-readablemedium operating in an edge device having computer instructions toreceive a Session Initiation Protocol (SIP) message from a user endpointdevice (UE) requesting communication services, and replace a commonerror message generated by a Server Office when unavailable to providecommunication services to the UE with an alternative error messageindicating a temporary unavailability of communication services.

FIGS. 1-2 depict illustrative embodiments of a communication system.FIG. 1 depicts a Next Generation Network (NGN) comprising networkelements that among other things can provide subscriber services such asVoice over Internet Protocol (VoIP), traditional Public Network SwitchedNetwork (PSTN), and a hybrid communications between VoIP and PSTNcommunication devices. NGN networks can have Access Offices which cancommunicate with subscriber devices in the form of user endpoint (UE)communication devices (herein referred to as UEs) over a Public Networkof a service provider. The Public Network can be third party ISPs thatprovide Internet access to UEs in the last mile. The Access Offices caninclude among other things a Session Border Controller (S/BC) forinterfacing with the UEs and thereby providing communication servicesthereto by way of a Proxy Call Session Control Function (P-CSCF) whichcommunicates with a Server Office over an Internal Network of theservice provider such as a Multi-Protocol Label Switching (MPLS)network. The MGW can be used to support hybrid communications betweenthe UEs such as VoIP audio packets and PSTN TDM-based voice trunks.

The S/BC can submit communication requests initiated by the UEs to theServer Office via a P-CSCF. The Server Office in turn can manage suchrequests utilizing combinations of CSCFs, Application Servers, a MediaGateway Control Function (MGCF) which supports PSTN communications, anda Home Subscriber Server (HSS). The network elements of the ServerOffice singly or in combination provide resources to establishcommunications between UEs of a VoIP or PSTN type. The service providerof the communication network of FIG. 1 can provision the UEs by way ofDomain Name Systems (DNS) servers which can be programmed by the serviceprovider as desired.

The UEs are provisioned by the service provider with necessaryinformation to connect to the NGN communication network of FIG. 1 and toobtain services therefrom. The UEs can request additional contactinformation of the service provider network from DNS servers on aperiodic basis. The information can include information associated witha primary or secondary S/BC of one or more Access Office. As will beshown, the UE preferably registers with an Access Office with theprimary S/BC. As shown in FIG. 2, the UE can register with the secondaryS/BC as a means to mitigate a communication fault experienced by anetwork element of an Access Office or a Server Office which causesinterruption in communication services provided to the UE.

FIG. 3 depicts an illustrative embodiment of provisioning information inthe form of DNS Serve (SRV) records conforming to standards promulgatedby the Internet Engineering Task Force (IETF). FIG. 3 illustrates afirst logical Fully Qualified Domain Name (FQDN) associated with a WestRegion of the United States configured in such a manner that UEs in theWest Region are primarily served by a Server Office located in Dallas.FIG. 3 further illustrates a second logical FQDN associated with an EastRegion of the United States configured in such a manner that UEs in theEast Region are primarily served by a Server Office located inPhiladelphia. Each logical FQDN can comprise primary and secondary SRVrecords for directing UEs to a primary or secondary S/BC, respectively,operating in a corresponding Access Office. For illustration purposesonly, the first logical FQDN is represented by the characterstring_sip._udp.sbcwest.att.net, while the second logical FQDN isrepresented by the character string_sip._udp.sbceast.att.net. Anydesirable character arrangement is possible for defining an FQDN.

A UE can be provisioned for example with a logical FQDN such as_sip._udp.sbcwest.att.net (or the other) shown in FIG. 3 by common means(e.g., at point of sale, over-the-air programming for wirelesscommunication devices such as cellular phones, or by way of wirelineprovisioning). Once it is provisioned, a UE can query a DNS server forthe SRV records associated with its logical FQDN according to the flowdiagram of FIG. 4. As shown in the flow diagram, the DNS server cansupply SRV records responsive to a query with the logical FQDN_sip._udp.sbcwest.att.net.

The priority of the first SRV record, designated by the field with thenumber “0”, supersedes the priority of the second SRV record designatedby the field with the number “1”. Accordingly the A-recordims-core1.att.net supplied by the DNS server for the first SRV recordcorresponds to the primary S/BC, while the A-record ims-core2.att.netsupplied by the DNS server for the second SRV record corresponds to thesecondary S/BC. It should be noted that the primary and secondary S/BC'sis determined by the priority field of the SRV records not the order ofthe SRV records shown in FIG. 3.

With the primary and secondary A-records, a UE assigned to the WestRegion FQDN (_sip._udp.sbcwest.att.net) can proceed to request the IPaddress of the primary S/BC (142.30.79.10) followed by the IP address ofthe secondary S/BC (142.30.89.10). Since the primary SRV record has ahigher priority than the secondary SRV record, the UE chooses toregister with the primary S/BC as shown in the illustration of FIG. 4,which in this example is situated in Dallas. If the UE is unable toregister with the primary S/BC, it reverts to the secondary S/BC asdepicted in the call flow diagram of FIG. 5.

It should be noted that the logical FQDN can be associated with any S/BCof any Access Office. Referring back to FIG. 3, the logical FQDN of theEast Region (_sip._udp.sbceast.att.net) is programmed with a reverseorder of the primary and secondary SRV records of the FQDN(_sip._udp.sbcwest.att.net) of the West Region. Thus a UE provisionedwith the logical FQDN of the East Region shown in FIG. 3 will registerwith the primary S/BC situated in Philadelphia, and will rely on thesecondary S/BC situated in Dallas for backup services. As such, UEs inthe East region, provisioned with _sip._udp.sbceast.att.net, will useims-core2.att.net since it has the priority 0, which is the higherpriority.) The ability to associate the logical FQDN with any S/BC ofany region or Access Office provides a service provider a means tomanage the distribution and reallocation of UEs in an NGN network.

Method 600 of FIG. 6 depicts an illustrative embodiment for managingcommunication services of UEs in an NGN network. Method 600 can beginwith step 602 in which a UE sends a SIP message to an Edge Device. TheSIP message can represent a request to establish a communication sessionwith another UE. In this step the UE submits the SIP message towhichever Edge Device it has registered with previously (e.g., a primaryS/BC or a secondary S/BC). FIG. 6 presents five illustrative scenariosthat can arise from step 604. Each scenario depicts how network elementsof the NGN network and/or UE address communication requests undervarious conditions.

Method 600 of FIG. 6 depicts an illustrative embodiment for managingcommunication services of UEs in an NGN network. Method 600 can beginwith step 602 in which a UE sends a SIP message to an Edge Device. TheSIP message can represent a request to establish a communication sessionwith another UE or a request to register with the primary S/BC. In thisstep the UE submits the SIP message to whichever Edge Device it hasregistered with previously (e.g., a primary S/BC or a secondary S/BC).FIG. 6 presents five illustrative scenarios that can arise from step604. Each scenario depicts how network elements of the NGN networkand/or UE address communication requests under various conditions.

Beginning with scenario 1, the UE may encounter in step 606 a situationin which the Edge Device is non-responsive. Such a situation can arisefrom the S/BC malfunctioning, the P-CSCF malfunctioning, an IP transportnetwork problem between the UE and the Edge device, or some other faultthat would prevent the UE from communicating with the Edge Device. FIG.7 depicts this scenario and the subsequent steps that may follow.Generally, the UEs can be programmed to monitor the response time of theEdge Device. If no response is received after a pre-defined timer (atimeout condition), the UE can proceed to steps 610-612 to register withan alternative Edge Device which (e.g., a secondary S/BC).

The failover registration process can occur as described in the callflow diagram of FIG. 5. Once service is restored, the UE can resubmit aSIP message at step 602 to attempt again to establish communicationswith a targeted UE. Scenario 2 represents a successful attempt by the UEto request communication services. If the alternative Edge Devicesuccessfully forwards the SIP message to a Server Office, and the ServerOffice is available, it can provide the UE in step 614 the communicationservices requested. As a result of step 614, the UE can establishcommunications with a targeted UE.

Scenario 3 depicts another scenario which may be encountered by the UE,which is illustrated in FIG. 8. Certain conditions such as a fault incomputing or communication resources may prevent the Edge Device fromprocessing the SIP message request submitted by the UE. In thissituation, the Edge Device can transmit to the UE in step 616 an errormessage such as a SIP 503 code message which can represent a serviceunavailable condition as defined by IETF standards. Under thesecircumstances, the UE can resort to registering with an alternative EdgeDevice according to steps 610-612. Once service is available, the UE cansubmit another SIP message request in step 602 which may result in asuccessful communication session as a result of step 614.

Scenario 4 depicts yet another scenario which may be encountered by theUE, illustrated in FIG. 9. In this illustration, the Edge Device in step618 forwards the SIP message request to the Server Office, but receivesin step 620 an error message from the Server Office in the form of a 5XXor 6XX SIP code indicating a condition in which a call processing serverin the Server Office, e.g., MGCF, or S-CSCF, is unable to providecommunication services to the UE due to due to server fault or resourceoverload. In step 622 the Edge Device however determines that the erroris not a condition that would require the UE to fail over to anotherserver office. That is, the responsible call processing server may beexperiencing a fault condition which may be temporary.

To prevent the UE from resorting to registering with an alternative EdgeDevice as described by steps 610-612, the Edge Device in step 622replaces the 5XX/6XX SIP code with a 480 SIP code. A 480 SIP codedescribes a communication state corresponding to a temporaryunavailability of communication services. As a result of transmittingthe 480 SIP code to the UE, the UE generates a fast busy signal, whichdoes not invoke a failover procedure. The UE can be directed to resubmitanother SIP message request in step 602 at a later time. On a subsequentattempt the Server Office may be available to provide the requestedcommunication services.

It should be noted that prior art Edge Devices would have forwarded tothe UE the error message generated by the Server Office. Had thishappened, the UE would have registered with an alternative Edge Deviceas described by steps 610-612. By replacing the SIP error message of theServer Office in step 622, the Edge Device has likely prevented anunnecessary rehoming of the UE, which is an effective method forreducing false alarms submitted to UEs. The present method can make anNGN network more stable by preventing a large number of UEs fromexecuting unnecessary geographical failover procedures.

Scenario 5 depicts another scenario which may be encountered by the UEas shown by the illustration of FIG. 10. In this illustration, the EdgeDevice in step 626 detects that the Server Office is out of service orunreachable. The out of service condition can arise from faulty IPtransport network connectivity between the Edge device and the serveroffice, or a server office experiencing a power hit or natural disasterhit which prevents the edge device from communicating with the serveroffice. Once detected, the Edge Device returns to the UE in step 628 aSIP error message in the form of a 5XX or 6XX SIP code to indicateservice is unavailable. Under these circumstances, the UE resorts toregistering to with an alternative Edge Device according to steps610-612, and reattempts a request for communication services in step 602as described earlier.

FIG. 11 depicts a generalization of a method 1100 operating in the EdgeDevice of FIGS. 1-2. Once the Edge Device is in a ready state in step1102, it can process SIP messages received from UEs or from the internalserver offices in step 1104. If Edge Device detects in step 1106 thatthe SIP message is not from a UE operating of the service providernetwork, or an error response has been received that is not a 5xx or 6xxSIP code, then the Edge Device proceeds to step 1110 where it processthe SIP message as defined by the IETF standards. On the other hand, ifthe SIP message is from a service provider network's server office, andan error response has been received with a 5xx or 6xx SIP code, then theEdge Device proceeds to step 1112 where it constructs a new SIP 480error message using the information in the received error message, andsends the SIP 480 error message to the requesting UE, thereby causingsubsequent actions in the UE as described in FIG. 6.

From the foregoing descriptions, it would be evident to an artisan withordinary skill in the art that the aforementioned embodiments can bemodified, reduced, or enhanced without departing from the scope andspirit of the claims described below. Accordingly, the reader isdirected to the claims for a fuller understanding of the breadth andscope of the present disclosure.

FIG. 12 depicts an exemplary diagrammatic representation of a machine inthe form of a computer system 1200 within which a set of instructions,when executed, may cause the machine to perform any one or more of themethodologies discussed above. In some embodiments, the machine operatesas a standalone device. In some embodiments, the machine may beconnected (e.g., using a network) to other machines. In a networkeddeployment, the machine may operate in the capacity of a server or aclient user machine in server-client user network environment, or as apeer machine in a peer-to-peer (or distributed) network environment.

The machine may comprise a server computer, a client user computer, apersonal computer (PC), a tablet PC, a laptop computer, a desktopcomputer, a control system, a network router, switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. It will beunderstood that a device of the present disclosure includes broadly anyelectronic device that provides voice, video or data communication.Further, while a single machine is illustrated, the term “machine” shallalso be taken to include any collection of machines that individually orjointly execute a set (or multiple sets) of instructions to perform anyone or more of the methodologies discussed herein.

The computer system 1200 may include a processor 1202 (e.g., a centralprocessing unit (CPU), a graphics processing unit (GPU, or both), a mainmemory 1204 and a static memory 1206, which communicate with each othervia a bus 1208. The computer system 1200 may further include a videodisplay unit 1210 (e.g., a liquid crystal display (LCD), a flat panel, asolid state display, or a cathode ray tube (CRT)). The computer system1200 may include an input device 1212 (e.g., a keyboard), a cursorcontrol device 1214 (e.g., a mouse), a disk drive unit 1216, a signalgeneration device 1218 (e.g., a speaker or remote control) and a networkinterface device 1220.

The disk drive unit 1216 may include a machine-readable medium 1222 onwhich is stored one or more sets of instructions (e.g., software 1224)embodying any one or more of the methodologies or functions describedherein, including those methods illustrated above. The instructions 1224may also reside, completely or at least partially, within the mainmemory 1204, the static memory 1206, and/or within the processor 1202during execution thereof by the computer system 1200. The main memory1204 and the processor 1202 also may constitute machine-readable media.

Dedicated hardware implementations including, but not limited to,application specific integrated circuits, programmable logic arrays andother hardware devices can likewise be constructed to implement themethods described herein. Applications that may include the apparatusand systems of various embodiments broadly include a variety ofelectronic and computer systems. Some embodiments implement functions intwo or more specific interconnected hardware modules or devices withrelated control and data signals communicated between and through themodules, or as portions of an application-specific integrated circuit.Thus, the example system is applicable to software, firmware, andhardware implementations.

In accordance with various embodiments of the present disclosure, themethods described herein are intended for operation as software programsrunning on a computer processor. Furthermore, software implementationscan include, but not limited to, distributed processing orcomponent/object distributed processing, parallel processing, or virtualmachine processing can also be constructed to implement the methodsdescribed herein.

The present disclosure contemplates a machine readable medium containinginstructions 1224, or that which receives and executes instructions 1224from a propagated signal so that a device connected to a networkenvironment 1226 can send or receive voice, video or data, and tocommunicate over the network 1226 using the instructions 1224. Theinstructions 1224 may further be transmitted or received over a network1226 via the network interface device 1220.

While the machine-readable medium 1222 is shown in an example embodimentto be a single medium, the term “machine-readable medium” should betaken to include a single medium or multiple media (e.g., a centralizedor distributed database, and/or associated caches and servers) thatstore the one or more sets of instructions. The term “machine-readablemedium” shall also be taken to include any medium that is capable ofstoring, encoding or carrying a set of instructions for execution by themachine and that cause the machine to perform any one or more of themethodologies of the present disclosure.

The term “machine-readable medium” shall accordingly be taken toinclude, but not be limited to: solid-state memories such as a memorycard or other package that houses one or more read-only (non-volatile)memories, random access memories, or other re-writable (volatile)memories; magneto-optical or optical medium such as a disk or tape;and/or a digital file attachment to e-mail or other self-containedinformation archive or set of archives is considered a distributionmedium equivalent to a tangible storage medium. Accordingly, thedisclosure is considered to include any one or more of amachine-readable medium or a distribution medium, as listed herein andincluding art-recognized equivalents and successor media, in which thesoftware implementations herein are stored.

Although the present specification describes components and functionsimplemented in the embodiments with reference to particular standardsand protocols, the disclosure is not limited to such standards andprotocols. Each of the standards for Internet and other packet switchednetwork transmission (e.g., TCP/IP, UDP/IP, HTML, HTTP) representexamples of the state of the art. Such standards are periodicallysuperseded by faster or more efficient equivalents having essentiallythe same functions. Accordingly, replacement standards and protocolshaving the same functions are considered equivalents.

The illustrations of embodiments described herein are intended toprovide a general understanding of the structure of various embodiments,and they are not intended to serve as a complete description of all theelements and features of apparatus and systems that might make use ofthe structures described herein. Many other embodiments will be apparentto those of skill in the art upon reviewing the above description. Otherembodiments may be utilized and derived therefrom, such that structuraland logical substitutions and changes may be made without departing fromthe scope of this disclosure. Figures are also merely representationaland may not be drawn to scale. Certain proportions thereof may beexaggerated, while others may be minimized. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the above description.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separately claimed subject matter.

What is claimed is:
 1. A method, comprising: receiving, by a systemcomprising a processor, a session initiation protocol message from auser endpoint device requesting communication services, wherein the userendpoint device is communicatively coupled to a backup session bordercontroller; forwarding the session initiation protocol message to anetwork element of a primary server office; receiving a first errormessage from the network element; analyzing the first error message;detecting a status of the primary server office, wherein the status isselected from the group consisting of a first error status and a seconderror status determined from the analyzing of the first error message;replacing the first error message with a second error message andtransmitting the second error message to the user endpoint deviceresponsive to the status being the first error status, wherein thetransmitting of the second error message to the user endpoint deviceprevents the user endpoint device from performing a failoverregistration to the backup session border controller; and transmittingthe first error message to the user endpoint device responsive to thestatus being the second error status, wherein the transmitting of thefirst error message to the user endpoint device causes the user endpointdevice to perform the failover registration to the backup session bordercontroller, wherein the first error status indicates the primary serveroffice is temporarily out of service, and wherein the user endpointdevice is a telephone.
 2. The method of claim 1, wherein the forwardingof the session initiation protocol message, the receiving of the firsterror message, and the detecting of the status are performed by thesystem.
 3. The method of claim 1, wherein the replacing of the firsterror message with the second error message and the transmitting of thesecond error message, and the transmitting of the first error messageare performed by the system.
 4. The method of claim 1, wherein thesecond error status indicates the primary server office is out ofservice.
 5. The method of claim 1, wherein the first and second errormessages correspond to first and second session initiation protocolerror messages.
 6. The method of claim 5, wherein the first sessioninitiation protocol error message comprises a 5XX session initiationprotocol code or a 6XX session initiation protocol code to indicatecommunication services are unavailable.
 7. The method of claim 5,wherein the second session initiation protocol error message comprises a480 session initiation protocol code to indicate communication servicesare temporarily unavailable.
 8. The method of claim 1, wherein the userendpoint device generates a busy signal responsive to the transmittingof the second error message to the user endpoint device.
 9. A method,comprising: transmitting, by a system comprising a processor, a sessioninitiation protocol message to a primary session border controller forrequesting communication services for a user endpoint device; receivingan error message from the primary session border controller; analyzingthe error message; detecting a status, wherein the status is selectedfrom the group consisting of a first error status and a second errorstatus determined from the analyzing of the error message; and disablinga failover registration by the user endpoint device to a backup sessionborder controller by replacing the received error message with areplacement message that prevents the failover registration responsiveto the status being the first error status, wherein the first errorstatus is associated with the communication services being temporarilyout of service, and wherein the system is the user endpoint device. 10.The method of claim 9, wherein the receiving of the error message, theanalyzing of the error message, and the detecting of the status areperformed by the system.
 11. The method of claim 9, wherein thedisabling of the failover registration is performed by the system. 12.The method of claim 9, wherein the second error status is associatedwith the communication services being out of service.
 13. The method ofclaim 9, wherein the received error message comprises a sessioninitiation protocol error message comprising a 480 session initiationprotocol code to indicate communication services are temporarilyunavailable.
 14. The method of claim 9, comprising enabling the failoverregistration by the user endpoint device to the backup session bordercontroller by transmitting the error message to the user endpoint deviceresponsive to the status being the second error status.
 15. The methodof claim 9, wherein the error message comprises a session initiationprotocol error message comprising a 5XX session initiation protocol codeor a 6XX session initiation protocol code to indicate communicationservices are unavailable.
 16. The method of claim 9, wherein the userendpoint device generates a busy signal responsive to receiving thereplacement message.
 17. A method, comprising: receiving a sessioninitiation protocol message from a user endpoint device requestingcommunication services; forwarding the session initiation protocolmessage to a network element of a primary server office; receiving anerror message from the network element; determining from the errormessage whether the primary server office is out of service; andreplacing the error message with a replacement message to prevent theuser endpoint device from performing a failover registration to a backupsession border controller responsive to determining that the primaryserver office is partially out of service, wherein the receiving sessioninitiation protocol message, the forwarding the session initiationprotocol message, the receiving the error message, the determining fromthe error message whether the primary server office is out of service,and the replacing of the error message are performed by a primarysession border controller, and wherein the primary server office is outof service when the error message comprises a session initiationprotocol error message comprising one of a 5XX session initiationprotocol code and a 6XX session initiation protocol code.
 18. The methodof claim 17, wherein the replacement message comprises a second errormessage that causes the user endpoint device to assert a busy signal.19. The method of claim 17, further comprising transmitting the errormessage to the user endpoint device to cause the user endpoint device toperform a failover registration to the backup session border controllerresponsive to determining that the primary server office is out ofservice.
 20. The method of claim 17, wherein the primary server officeis partially out of service when the error message comprises a 480session initiation protocol code.